Despite several decades of research, no unifying hypothesis for a molecular/cellular basis of action for antidepressant drugs (or depressive disorders) has emerged. Over the last several years, we have suggested that, in addition to pre-synaptic targets (uptake sites), a number of antidepressant drugs have a post-synaptic mechanism of action. Toward this end, we have observed that chronic treatment of C6 glioma cells with a number of chemically diverse antidepressant compounds moves the heterotrimeric G protein Gsa out of lipid rafts and into a closer association with adenylyl cyclase. We have also seen that the interaction between Gsa and tubulin, an element of the cytoskeleton, is diminished by antidepressant treatment in this model system. This study will examine the antidepressant-induced movement of Gsa out of lipid rafts and the consequences of this for G protein signaling systems and, ultimately, for development of synaptic structures. Many of the experiments will be done in real-time (over a period of days) using florescent G protein analogs as well as fluorescent cytoskeletal proteins and lipid raft markers. These studies will be carried out in neural and glial cell lines as well as in primary rat hippocampal neurons. These studies will also endeavor to establish the relevance of this process for antidepressant action, by developing probes designed to disrupt aspects of the interaction between Gsa and tubulin and determining whether such probes have antidepressant properties in our model system. This molecular interaction as well as altered interaction between Gsa and lipid rafts may prove to be a biological marker for both depression and for successful antidepressant treatment. It is hoped that successful completion of this study will not only reveal possible molecular mechanisms for the etiology and treatment of depression, but will point the way to new, proteomic-based strategies for treatment. The burden of depression, both from a societal and economic standpoint, ranks second only to ischemic heart disease. We have developed a model system, using cultured cells, to determine the effectiveness of antidepressant treatment and to ascertain a mechanism whereby so many different drugs can be used to treat the same disorder. These studies should help to identify molecular pathways for both depression and the actions of antidepressant drugs. Understanding these should reveal both biological markers for depression and new classes of compounds to treat this disorder.